Panorama Research, Inc. is developing a novel means of eradicating dental caries using passive immunization with a plant-produced secretory IgA antibody (sIgA) that inhibits binding of Streptococcus mutans to teeth. Results of a recently completed phase II pilot study demonstrate that this sIgA, named CarnRx(TM), can eliminate S. mutans for long periods of time. Based on this work and IND has been filed in the USA. The goal of the present proposal is to develop a simple, homogeneous test to detect residual S. mutans rapidly and accurately. This test is expected to be used in conjunction with CaroRx(TM) treatment, in the dental office or by the patient, for facile assessment of efficacy and monitoring of reinfection by S. mutans. For the development of this test, we will use a variant of beta- galactosidase, whose activity has been engineered to depend on the interaction of heterologous proteins fused to otherwise non- complementing fragments of the enzyme. We will fuse the fragments to antibody fragments which recognize abundant, specific epitopes on the surface of S. mutans, such that high-density binding of the chimeric fragments to the bacterial cell surface will allow trace numbers of cells to be readily detectable with chromogenic beta-galactosidase substrates. PROPOSED COMMERCIAL APPLICATION: The primary goal of this work is to provide a simple, rapid, accurate, and convenient test for oral cariogenic bacteria, which can be used in the home or dentist's office for facile caries risk assessment.